1. Field of the Invention
The present invention relates to an apparatus of the type including a grip sensor for controlling the number of revolutions of an engine and more particularly to an apparatus for controlling the number of revolutions of an engine mounted on a construction machine such as power shovel, wheel loader in dependence on the working condition of the construction machine.
2. Description of the Prior Art
A construction machine such as power shovel or the like performs digging operation, loading operation or the like while the number of revolutions of an engine mounted thereon is kept at a certain fixed level corresponding to an idle operative state that is set to a high level. On the other hand, a construction machine such as crane, wheel loader or the like is so constructed that the number of revolutions of an engine mounted thereon is adjusted by the depression of an acceleration pedal so as to control speed of operation when working, according to the power required for performing the operation.
However, it has been pointed out in problems with respect to the conventional operation of the power shovel that due to existence of inoperative periods of time such as when waiting for the arrival of a dump truck or the like, the rate of fuel consumption increases when the number of revolutions of an engine is kept at a fixed level corresponding to the high idle operative state. Moreover a noise level is maintained at a high level during the waiting time in which no field operation is performed. However, it is very troublesome for an operator to reduce the number of revolutions of an engine to a lower level by lowering the idle operative state with the use of a fuel adjusting lever each time no field operation is being performed.
In the case of crane, wheel loader or the like, adjusting of an extent of acceleration in dependence on the current state of load is troublesome for an operator and it is often found that engine trouble takes place when an extent of acceleration is not determined properly. In view of the facts as mentioned above, there have already been some proposal such as presetting the number of revolutions of an engine in an idle state to a higher level, modification of engine performances of engine torque and horse power. However, when the number of revolutions of an engine is raised up during idle operative state, the same incovenience takes place as in the case of power shovel.
As is hitherto known, power shovel or the like construction machine is provided with an automatic deceleration device which is intended to reduce the number of revolutions of an engine to a level lower than a predetermined number of revolutions by actuating a fuel adjusting lever during inoperative time, that is, during no load operation of the engine in order to reduce fuel consumption and prevent generation of noisy sound.
However, since the automatic deceleration device includes a limit switch for mechanically detecting the running state of power shovel and the neutral state of control levers for controlling actuation of working tools such as bucket or the like so as to detect an inoperative state where an operator does not operate power shovel and moreover it includes a pressure switch for detecting lower pressure state of supplied hydraulic oil (inoperative state of the control levers) in association with actuation of the control levers, the number of revolutions of an engine is automatically caused to decrease when the control levers are shifted to the neutral position, in spite of the fact that an operator still intends to continue the operation. This means that function of the automatic deceleration device conflicts with labor intention of an operator.
In the case of a construction machine such as crane, wheel loader or the like which is so constructed that the number of revolutions of an engine mounted thereon is adjusted as required by selectively determining an extent of depressing of an acceleration pedal, there has not been made any proposal as to how the number of revolutions of the engine is automatically controlled in dependence on the existent operative state.